Zu den Oberflächentemperaturen der Nordsee im Jahr 1993     

Gerd Wegner 《Ocean Dynamics》1994,46(2):163-175

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Impact of Climate Change on the Regional Hydrology – Scenario-Based Modelling Studies in the German Rhine Catchment     

Lucas Menzel  Annegret H. Thieken  Daniel Schwandt  Gerd Bürger 《Natural Hazards》2006,38(1-2):45-61

The aim of the study is an impact analysis of global climate change on regional hydrology with special emphasis on discharge conditions and floods. The investigations are focussed on the major part of the German Rhine catchment with a drainage area of approx. 110,000 km². This area is subdivided into 23 subcatchments. In a first step, the hydrological model HBV-D serves to simulate runoff conditions under present climate for the individual subbasins. Simulated, large scale atmospheric fields, provided by two different Global Circulation Models (GCMs) and driven by the emission scenario IS95a (“business as usual”) are then used as input to the method of expanded downscaling (EDS). EDS delivers local time series of scenario climate as input to HBV-D. In a final step, the investigations are focussed on the assessment of possible future runoff conditions under the impact of climate change. The study indicates a potential increase in precipitation, mean runoff and flood discharge for small return intervals. However, the uncertainty range that originates from the application of the whole model chain and two different GCMs is high. This leads to high cumulative uncertainties, which do not allow conclusions to be drawn on the development of future extreme floods.  相似文献   

Characteristics and dynamics of multiple intertidal bars,north Lincolnshire,England     

Selma van Houwelingen  Gerhard Masselink  Joanna Bullard 《地球表面变化过程与地形》2006,31(4):428-443

Multiple intertidal bars and troughs, often referred to as ‘ridges and runnels’, are significant features on many macrotidal sandy beaches. Along the coastline of England and Wales, they are particularly prevalent in the vicinity of estuaries, where the nearshore gradient is gentle and a large surplus of sediment is generally present. This paper examines the dynamics of such bar systems along the north Lincolnshire coast. A digital elevation model of the intertidal morphology obtained using LIDAR demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m. The largest and most pronounced bars (height = 0·5–0·8 m) are found around mean sea level, whereas the least developed bars (height = 0·2–0·5 m) occur in the lower intertidal zone. Annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates; however, there is little resemblance between concurrent photographs, and ‘resetting’ of the intertidal profile occurs on an annual basis. Three‐dimensional beach surveys were conducted monthly at three locations along the north Lincolnshire coast over a one‐year period. The intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions, and bars are least numerous and flattest during the more energetic winter months. Morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month. The behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors (e.g. incident wave energy, different types of wave processes, longshore and cross‐shore sediment transport), relaxation time and morphodynamic feedback. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

On the stability of geotechnical systems and its fractal progressive loss     

Gerd Gudehus  Asterios Touplikiotis 《Acta Geotechnica》2018,13(2):317-328

Geotechnical systems, consisting of soil and embedded solid structures, are practically stable if inevitable actions cause at most harmless redistributions. This kind of robustness can often be achieved with limit state design, i.e. by assuming representative snapshots of worst cases. Changes in configuration and state due to changing boundary conditions can be better judged with quasi-static numerical simulations using validated constitutive relations. The ever-present fractality of the ground may be neglected as long as the system is stable, whereas it gets dominant during a progressive loss of stability with jerky critical phenomena which elude mathematical treatment until present. In this sense geotechnical systems can be or get sensitive, i.e. further actions can trigger detrimental chain reactions with seismogeneous collapse of the soil fabric, pore pressure increase up to liquefaction, erosion, cracking of ground and structural parts and/or tilting. The geotechnical risk can be better mitigated by taking into account chain reactions with wild randomness. It can be further reduced by monitoring the seismic emission in addition to mass flows, structural deformations and pore pressures. The paper is to clarify notions and concepts.  相似文献   

The Atmospheric Boundary Layer Over Baltic Sea Ice   总被引：4，自引：0，他引：4  

Burghard?BrümmerEmail author  Amèlie?Kirchg??ner  Gerd?Müller 《Boundary-Layer Meteorology》2005,117(1):91-109

A new parametrization for the surface energy balance of urban areas is presented. It is shown that this new method can represent some of the important urban phenomena, such as an urban heat island and the occurrence of a near-neutral nocturnal boundary layer with associated positive turbulent heat fluxes, unlike the traditional method for representing urban areas within operational numerical weather prediction (NWP) models. The basis of the new parametrization is simple and can be applied easily within an operational NWP model. Also, it has no additional computational expense compared to the traditional scheme and is hence applicable for operational forecasting requirements. The results show that the errors for London within the Met Office operational mesoscale model have been significantly reduced since the new scheme was introduced. The bias and root-mean-square (rms) errors have been approximately halved, with the rms error now similar to the model as a whole. The results also show that a seasonal cycle still exists in the model errors, but it is suggested that this may be caused by anthropogenic heat sources that are neglected in the urban scheme.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.  相似文献   

Reconstruction of palaeohydrological conditions in a lagoon during the 2nd Zechstein cycle through simultaneous use of δD values of individual n-alkanes and δ<Superscript>18</Superscript>O and δ<Superscript>13</Superscript>C values of carbonates     

Dirk?Sachse  Jens?Radke  Reinhard?Gaupp  Lorenz?Schwark  Guido?Lüniger  Gerd?GleixnerEmail author 《International Journal of Earth Sciences》2004,93(4):554-564

For the first time ¹⁸O and ¹³C values from carbonates and D values of individual n-alkanes were used to reconstruct palaeohydrological conditions in a lagoon at the southern margin of the Central European Zechstein Basin (CEZB). A 12-m core covering the complete Ca2 interval and adjacent anhydrites (A1 and A2) was analyzed for ¹⁸O and ¹³C values of dolomitized carbonates and D values of individual n-alkanes. ¹⁸O_carb values (+2 to +5 vs. VPDB) were strongly influenced by evaporation and temporal freshwater input into the lagoon. The ¹³C_carb values (–1 to +4 vs. VPDB) were controlled mainly by changes in primary production. Both isotopic ratios show an inverse relationship throughout most of the core, contradicting diagenetic alteration, since ¹³C_carb values are not altered significantly during dolomitization. Assuming a temperature range of 35–40 °C in the lagoon, ¹⁸O_carb values of +2.5 to +8 (vs. VSMOW) for the lagoonal water can be reconstructed. The lagoon may have desiccated twice during the Ca2 interval, as indicated by very high ¹⁸O_carb and low ¹³C_carb values, coinciding with increasing amount of anhydrite in the analyzed sample. These events seem to reflect not just local but a regional intra-Ca2 cyclicity. Measured D values of the short-chain n-alkanes, namely n-C₁₆ and n-C₁₈ which are widely used as indicators for photosynthetic bacterial and algal input, reflect the isotopic composition of the lagoonal water. Assuming constant fractionation during incorporation of hydrogen into lipids of –160, an average D value of +70 (vs. VSMOW) can be reconstructed for the lagoonal water, accounting for very arid conditions. The long-chain n-alkanes n-C₂₇, n-C₂₈, n-C₂₉ and n-C₃₀, thought to be derived from the leaf waxes of terrestrial higher plants, were shown to be depleted in D relative to the short-chain alkanes, therefore indicating a different hydrogen source. Terrestrial plants in arid areas mainly use water supplied by precipitation. By using a smaller fractionation of –120 due to evaporation processes in the leaves, reconstructed values vary between –74 and –9 (vs. VSMOW). These values are not indicating extremely arid conditions, implying that the long-chain n-alkanes were transported trough wind and/or rivers into the lagoon at the Zechstein Sea coast. D_water values, reconstructed using the n-C₁₆ alkane and ¹⁸O _water values, independently reconstructed on the same sample using the temperature dependant fractionation for dolomites are good agreement and suggest high amounts of evaporation affecting the coastal lagoon. Altogether, our results indicate that hydrogen isotopic ratios of n-alkanes give information on their origin and are a useful proxy for palaeoclimatic reconstruction.  相似文献   

Sea surface temperature changes in the North Sea and their causes   总被引：2，自引：0，他引：2  

Becker  Gerd A.; Pauly  Manfred 《ICES Journal of Marine Science》1996,53(6):887-898

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Thermal history of the westernmost Eastern Alps (Penninic Rhenodanubian Flysch nappes,Helvetic nappes,and Subalpine Molasse thrust sheets)     

Michael Zerlauth  Audrey Bertrand  Gerd Rantitsch  Doris Groß  Hugo Ortner  Hannah Pomella  Bernhard Fügenschuh 《International Journal of Earth Sciences》2016,105(5):1525-1547

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Alongshore variation in beach cusp morphology in a coastal embayment     

Gerhard Masselink 《地球表面变化过程与地形》1999,24(4):335-347

The variation in beach cusp characteristics was examined along a 1 km long embayed beach (Pearl Beach, New South Wales, Australia). The beach cusp morphology had formed during the previous day and/or night and displayed a marked alongshore variation in cusp spacing. The edge wave mechanism of beach cusp formation could not account for the observed trend in cusp spacing, because no relationship could be established between the spacing of the cusps and the gradient of the beachface. On the other hand, the cusp spacing was strongly related to the horizontal swash excursion, providing some support for the self-organization model of beach cusp formation. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Climatology of noctilucent cloud radii and occurrence frequency using SCIAMACHY     

Charles E. Robert  Christian von Savigny  John P. Burrows  Gerd Baumgarten 《Journal of Atmospheric and Solar》2009,71(3-4):408-423

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